1. Field of the Invention
The present invention relates to a rotary kiln used to manufacture a battery material, and to a battery material manufactured by the rotary kiln.
2. Description of the Related Art
Secondary batteries are widely used as power sources for mobile devices such as cellular phones and laptop computers. The secondary batteries are also widely used as power sources for driving motors of hybrid vehicles, which have become increasingly popular in recent years from the viewpoint of environmental protection.
In the related art, a battery material for use as a cathode active material of the secondary batteries or the like is manufactured by a periodic kiln. In recent years, however, the need for the secondary batteries has been significantly increased as discussed above. Thus, a continuous kiln which has an excellent processing capacity compared to the periodic kiln is drawing attention. In general, SUS (Stainless Used Steel) with excellent heat resistance and excellent oxidation resistance is used as the material of a portion of the continuous kiln that contacts the battery material.
In the case where SUS is used as the material of the portion of the continuous kiln that contacts the battery material, however, metal scale such as Cr (chromium), Fe (iron), and Ni (nickel) in SUS may contaminate the battery material. This causes degradation in performance of the battery material.
Thus, each of Japanese Patent Application Publication No. 2003-119027 (JP-A-2003-119027) and Japanese Patent Application Publication No. 2003-267729 (JP-A-2003-267729) describes a manufacturing method for a battery material that can suppress contamination of a metal component. In the manufacturing method according to JP-A-2003-119027, a battery material is first manufactured by a rotary kiln, then the manufactured battery material is pulverized, and after that a magnetic force is applied to the pulverized battery material. That is, Fe scale and SUS scale are removed from the battery material by applying a magnetic force to the battery material. In the manufacturing method according to JP-A-2003-267729, an Al (aluminum) plating process is performed on the inner peripheral surface of a shell, which is made of SUS, of a rotary kiln. A coating is formed by the plating process on the inner peripheral surface of the shell. The coating suppresses contamination of Cr, Fe, and Ni from the shell made of SUS into the battery material.
However, the manufacturing method according to JP-A-2003-119027 requires a process for applying a magnetic force to the battery material. This reduces the production capacity. The manufacturing method also requires equipment that applies a magnetic force to the battery material. This increases the equipment cost.
In the manufacturing method according to JP-A-2003-267729, the coating formed on the inner peripheral surface of the shell may be exfoliated to expose the bare surface of the shell made of SUS. In this case, Cr, Fe, and Ni of the shell contaminate the battery material.